package scau.zzf.base;

public class IdWorker {

    private final long twepoch
            = 1288834974657L;
    private final long workerIdBits
            = 5L;
    private final long datacenterIdBits
            = 5L;
    private final long maxWorkerId
            = -1L ^ (-1L << workerIdBits);
    private final long maxDatacenterId
            = -1L ^ (-1L << datacenterIdBits);
    private final long sequenceBits
            = 12L;
    private final long workerIdShift
            = sequenceBits;
    private final long datacenterIdShift
            = sequenceBits + workerIdBits;
    private final long timestampLeftShift
            = sequenceBits + workerIdBits + datacenterIdBits;
    private final long sequenceMask
            = -1L ^ (-1L << sequenceBits);

    private long workerId;
    private long datacenterId;
    private long sequence
            = 0L;
    private long lastTimestamp
            = -1L;

    public IdWorker(long workerId) {
        new IdWorker(workerId, 0);
    }
    public IdWorker(long workerId, long datacenterId) {
        if (workerId
                > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(String.format("worker" +
                            "Id can't be greater than %d or less than 0",
                    maxWorkerId));
        }
        if (datacenterId
                > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter" +
                            "Id can't be greater than %d or less than 0",
                    maxDatacenterId));
        }
        this.workerId
                = workerId;
        this.datacenterId
                = datacenterId;
    }

    public synchronized String nextId() {
        long timestamp
                = timeGen();
        if (timestamp
                < lastTimestamp) {
            throw new RuntimeException(String.format("Clock" +
                            " moved backwards.  Refusing to generate id for %d milliseconds",
                    lastTimestamp - timestamp));
        }
        if (lastTimestamp
                == timestamp) {
            sequence
                    = (sequence + 1)
                    & sequenceMask;
            if (sequence
                    == 0) {
                timestamp
                        = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence
                    = 0L;
        }

        lastTimestamp
                = timestamp;

        return String.valueOf(((timestamp
                - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence);
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp
                = timeGen();
        while (timestamp
                <= lastTimestamp) {
            timestamp
                    = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }

    public static void main(String[] args) {
        IdWorker idWorker = new IdWorker(0);
        for (int i = 0; i < 1000; i++) {
            String id = idWorker.nextId();
            System.out.println(id);
        }
    }
}